Carbonyl metal plated product



ire Stats.

v F 3,055,98 Patented S p 25, 1962 3,055,087 CARBONYL METAL PLATEDPRODUCT Albert 0. Fink, Dayton, Ohio, assignor, by mesne assignments, toUnion Carbide Corporation, New York, N.Y., a corporation of New York NoDrawing. Fiied June 7, 1954, Ser. No.

435,086 5 Ciaims. (Ci. 29-1835) This invention deals with a method ofplating metals, and particularly with a method based on thedecomposition of gaseous metal carbonyls.

This application is a continuation-in-part of my copending application,Serial No. 85,941, filed April 6, 1949, now US. Patent No. 2,682,702,granted July 6, 1954, entitled Carbonyl Metal Plated Product.

In coatings obtained from metal carbonyls, the disadvantage heretoforehas frequently been encountered of the coating not sufiiciently adheringto the base metal. Moreover, the metal coating would become blistered ifthe object so coated was raised to elevated temperatures, for example, aheat treatment process.

It is an object of this invention to provide a method by Wliich theabove mentioned disadvantages are overcome.

In particular, it is an object of this invention to provide a method formetal plating by which a firmly adhering metal coating is obtained.

It is another object of this invention to provide a method of producingmetal coating which can withstand elevated temperatures withoutblistering.

It is still another object of this invention to provide a method ofproducing metal coatings which may be subjected to a heat-treatmentprocess without thereby impairing the adherence of the coating.

It is still another object of this invention to provide a product whosebase material is provided with a uniform deposited coat consisting oftwo separately deposited layers.

These and other objects are accomplished by carrying out the metaldeposition in two states in between which the base metal and its coatingare subjected to a de-gasification treatment carried out by subjectingthe material to heat.

In the first or initial step, only a very thin porous film is applied tothe metallic base by decomposing gaseous metal carbonyl. A layer of0.00001" to 0.00025, preferably of 0.00005 to 0.00015" in depth, wasfound most satisfactory for this initial coating. However, the inventionis not restricted to this particular range.

After this first layer has been applied, the coated article is heattreated. While applicant does not wish to be bound by theory, it isbelieved that the heat-treatment step effects desorption of gas whilethe coating is still in a porous state.

Since the porosity of a coating varies inversely as to thickness, andsince heat treatment of thick coatings applied at one time blisters anddeforms the coating, it is believed the theory developed fromdiscoveries giving rise to the instant invention presents an explanationaccounting for a portion if not the entire basis for non-adherence ofcoatings encountered heretofore.

The heat-treatment in no way involves heating to temperatures whichcause formation of alloys between the base and the metal coating.Microscopic examinations show no penetration into, for example, a copperbase by a nickel coating heated to 800 F.

The various methods of cleaning a base metal surface as by acid, alkali,bufiing, and the like, apparently diifer little in effect as regards theadherence of the coating. If the base to be coated is clean, thecoatings will have an adherence characteristic quickly determinable bysimple tests showing whether the single coating method or the doublecoating method of this invention was the plating system utilized.

In addition to grease, metal oxide films must be removed from bases suchas copper and aluminum. This film may be removed in the cleaning or bycontact within the plating chamber with reducing gases, for example,hydrogen, prior to introduction of decomposable carbonyl gases.

Inasmuch as identical cleaning steps have been used for identical baseswhich have been coated in one step and by the two step method of thisinvention, the pre-coating cleaning is not accountable for thedifference in the adhering character of the deposits.

Gases may be desorbed from the thinly coated bases by heating to atemperature in the range of 500 F. to 1200" F. depending upon thetemperature which can be applied to the base without softening ordestroying some characteristic such as temper or can be applied to thecoating.

For example, lead patterns should not be heated much above 550 F. while,on the other hand, alloy steels withstand temperatures in excess of 1200F. At the lower temperatures the heating is continued for a longer timein order to elfect comparative completeness of desorption.

Heating periods of 2 to 30 minutes have been found to be satisfactory.When heating a copper base covered with an initial coating of nickel, atreatment at a temperature of 800 to 900 F. for about 15 minutes wasfound most advantageous.

The intermediate heat-treatment may be carried out in a chamber undernon-oxidizing, but preferably under reduced atmosphere conditions.Nitrogen, carbon monoxide, carbon dioxide, hydrogen, natural gas,commercial brazing furnace gas, or mixtures of the above gases or othergases known in the art are suitable for this purpose.

One of the features of Well bonded coatings is their ability towithstand compression and expansion without breaking free from the base.Thus, any metal base which will withstand gas desorbing temperatures maybe coated by this carbonyl decomposition process.

Base materials which may be coated are, for example, copper, aluminum,magnesium, lead, cast iron, alloy steels, low carbon steels, non-ferrousalloys, such as bronze, brass, Monel metal and the like.

The process of this invention is applicable for plating with all metalswhich form gaseous carbonyls. Thus, plating with chromium, iron,tungsten, cobalt, molybdenum, tellurium, rhenium, and other metals maybe successfully carried out by the method described.

Each of these metal carbonyls has a temperature at which decompositionis complete. However, decomposition does take place slowly at lowertemperatures. For this reason it is preferred that the carbonyl bebrought into contact quickly with the base metal heated to a temperaturein the optimum decomposition range for each material.

In the case of tungsten, nickel, chromium, iron, We prefer to utilize atemperature in the range of 350 F. to 425 F, although temperatures belowand above this range may be utilized and still accomplish plating bydecomposition of carbonyl.

After the heat-treatment step a metal coating of the desired thicknessis applied to the pre-treated base by decomposing metal carbonyls.

The product thus obtained is characterized by an excellent bond and avery uniform and smooth surface structure. After the deposition of thecoating layer proper a second heat treating step may be applied.However, this is not obligatory. Sometimes an after-treatment isutilized to increase the ductility of the coating layer.

In the following, the process is described as applied to the coating ofvarious metal bases with a number of metals deposited from volatilemetal carbonyls.

Example I A copper plate was first mechanically cleaned by sanding.Thereafter the copper metal was heated to approxigaseous metaldeposition in accordance with the present invention as compared with wetelectroplating using electrolytic solutions are shown in the followingtabulation.

Metal Panels Plated Approximate Plate Type of Plating Remarks of withThickness, Inches Steel Nickel. 0.0004 Wet Electroplated This is typicalwet electroplating practice to secure adhesion and properties. Wetplating is slow, troubled with hydrogen embrittlement, uses electricity,and is a cumbersome process.

Do -do-.-.- 0.0004 deposited Nickel carbonyl gas The Gas Plating Processis not sub ect to hydrogen emover initial plated over initialbrittlement, uses gases not solutions contain ng electroheat-treatedcoating after lytes, is rapid, continuous and complete utilization ot0.00005 coating heat-treating at metallic compounds may be effected. ofnickel. 800 F.

Aluminum... .do. 0.0004 Wet Electroplated. Coatings of typicalelectroplate are both porous and brittle. A typical specimen of nickelhas a tensile strengthof 85,000 p.s.i. and an elongation of 3% which maybe 1.11- creased to 9% by annealing.

Do .do 0.0004 deposited Nickel carbonyl gas Coatings prepared by GasPlating are more ductile. For on initial heatplated over initialinstance, a specimen of nickel prepared by Gas Plat ng treated 0.00007coating after has a tensile strength of 93,000 ps1. and an elongationcoating of heat-treating at of 16% before annealing. nickel. 750 F.

mately 375 F. in an atmosphere containing approximately 1.4 percent byvolume of nickel carbonyl and diluted with carbon dioxide gas. The rateof gas flow was approximately 4 cubic feet per minute at a temperatureof 78 F. and 125 mm. Hg. The copper was exposed to this atmosphere forabout 2 minutes after which time a film of 0.00007" thickness had formedon the copper base. Thereafter the metal was heated in an atmosphere ofnatural gas to a temperature of about 800 F. for approximately minutes.

After these preliminary steps the coating proper was performed bysubjecting the metal to the same conditions and gases as in thepreliminary film-forming step. This second step was carried out forabout 15 minutes when a coating of 0.0004 had formed.

In order to increase the ductility of the coating, 1 subjected the metalto an additional heating step. This step consisted in heating for 15minutes to a temperature of from 800 F. to 900 F. in an atmosphere ofnatural gas.

Example II A lead pattern may be coated in the equipment utilized in theplating operation of Example I.

The lead pattern may be coated with iron deposited from iron carbonyl.The base may be heated to approximately 360 F. in an atmosphere ofnitrogen containing about 2 percent by volume of iron carbonyl. Afterexposure of the pattern to this atmosphere for about 2 minutes, thetemperature of the pattern may be raised to 525 F. and held there for 20minutes.

After these preliminary steps the final film-forming step may beperformed under the same conditions as is maintained in the preliminarycoating step.

Example [II An aluminum radar antenna may be coated in the sameequipment as is used in Examples I and II.

The aluminum may be treated with acid and then buffed to prepare cleansurfaces. The aluminum may be coated with nickel by heating the base toapproximately 375 F. in one minute with a feed rate of approximately 50cubic feet per hour of nickel carbonyl vapor diluted with hydrogen.

The initially coated base may be heat treated at 750 F. for 20 minutesto desorb gas. Following the heat treatment, the final coating and heattreating may follow exactly the pattern of Example I.

Example IV An SAE 1020 steel plate may be treated under similarconditions to Example I to plate the steel base with chromium depositedat a temperature of about 400 F.

Some of the important advantages and characteristic physical diflerencesobtained by so-called dry plating by The base metal panels in each casewere subjected to cleaning by washing in a cleaner composed of threeounces of sodium phosphate in a gallon of water, the solution beingheated to 200 F., and after washing the panels therein, rinsing the samein cold water.

The coatings obtained by the process of this invention on each of thebases of the examples are uniform in structure, free from blisters, andWell adhering to the base metal. Heat-treatment does not form blistersand impair the firm bond between the coating and the base metal.

In addition, apparatus such as the radar antenna of Example Ill, havebeen subjected to special tests under which the base suffered a 15percent elongation and withstood tensile strain of 90,000 pounds persquare inch before breaking. Up to the breaking point, the adheringcoating of nickel exhibited no checking or breaking tendency and thecoating parted in line with the point of failme of the base material.

It will be understood that this invention is not to be restricted to theexamples given in the specification, but that it is susceptible tovarious modifications and changes which come within the spirit of thedisclosure and the steps of the appended claims.

I claim:

1. A multi-layer metal product which is resistant to blistering andseparation of the layers upon heating the metal product at elevatedtemperatures comprising a first metal forming a base, a thin layer of asecond metal adhered to said base by exposing the base to an atmosphereof gaseous carbonyl formed from said second metal and having a thicknessof between about 0.00001 and 0.00025 inch, said thin layer being ofgreater porosity than said base metal, and having the gas thereindesorbed therefrom, and a further layer of said second metal disposedover said thin porous layer by exposing said thin layer to an atmosphereof gaseous carbonyl formed from said second metal, said further layerbeing substantially greater in thickness and higher in density than saidthin metal layer, and of a thickness of at least 0.0004 inch.

2. A multi-layer metal product which is resistant to blistering andseparation of the layers upon heating of the metal product at elevatedtemperatures comprising a lead metal base, a thin layer of iron adheredto said lead base by exposing the base to an atmosphere of gaseouscarbonyl formed from iron and having a thickness of between 0.00001 and0.00025 inch, said thin layer of iron being of greater porosity thansaid lead metal base and having the gas therein desorbed therefrom, andhaving a second layer of iron disposed over said thin porous layer byexposing the thin layer to an. atmosphere of gaseous carbonyl formedfrom iron, said second layer being substantially greater in thicknessand higher in density than said thin layer of iron.

3. A multi-layer metal product which is resistant to blistering andseparation of the layers upon heating of the metal product at elevatedtemperatures comprising a steel base, a thin layer of chromium adheredto said steel base by exposing the base to an atmosphere of gaseouscarbonyl formed from chromium and having a thickness of between about0.00001 and 0.00025 inch, said thin layer of chromium being of greaterporosity than said steel base, and having the gas therein desorbedtherefrom and a layer of chromium dispersed over said thin porous layerby exposing said thin layer to an atmosphere of gaseous carbonyl formedfrom chromium, said second layer being substantially greater inthickness and higher in density than said thin layer of chromium.

4. A multi-layer metal product which is resistant to blistering andseparation of the layers upon heating of the metal product at elevatedtemperatures comprising a Monel metal base, a thin layer of tungstenadhered to said Monel base by exposing the base to an atmosphere ofgaseous carbonyl formed from tungsten and having a thickness of betweenabout 0.00001 and 0.00025 inch, said thin layer of tungsten being ofgreater porosity than said Monel metal base and having all the gasdesorbed therefrom, and a second layer of tungsten disposed over saidthin porous layer by exposing the thin layer to an atmosphere of gaseouscarbonyl formed from tungsten, said second layer being greater inthickness and higher in density than said thin layer of tungsten.

5. A multi-layer metal product which is resistant to blistering andseparation of the layers upon heating the metal product at elevatedtemperatures comprising a first metal forming a base, a thin layer of asecond metal adhere to said base by exposing the base to an atmosphereof gaseous carbonyl formed :from said second metal and having athickness of between about 0.00001 and 0.00025 inch, said thin layerbeing of greater porosity than said base metal, and having the gastherein desorbed therefrom, and a further layer of said second metaldisposed over said thin porous layer by exposing said thin layer to anatmosphere of gaseous carbonyl formed from said second metal, saidfurther layer being substantially greater in thickness and higher indensity than said thin metal layer, and of a thickness of at least0.0004 inch, said first metal forming base being selected from the groupconsisting of steel, copper, aluminum, magnesium, lead and alloysthereof, and said second metal being selected from the group consistingof nickel, chromium, iron, tungsten, molybdenum, cobalt, tellurium andrhenium.

References Cited in the file of this patent UNITED STATES PATENTS1,931,704 Moore Oct. 24, 1933 1,998,496 Fiedler Apr. 23, 1935 2,053,096McKay Sept. 1, 1936 2,115,750 Rubin May 3, 1938 2,120,561 Laise June 14,1938 2,225,868 Huston Dec. 24, 1940 2,293,810 Domm Aug. 25, 19422,317,350 Adler et a1. Apr. 27, 1943 2,344,138 Drummond Mar. 14, 19442,391,457 Carlson Dec. 25, 1945 2,412,698 Van der Horst Dec. 17, 19462,412,977 Eskin Dec. 24, 1946 2,619,433 Davis et al Nov. 25, 19522,653,879 Fink Sept. 29, 1953 2,682,702 Fink July 6, 1954

1. A MULTI-LAYER METAL PRODUCT WHICH IS RESISTANT TO BLISTERING ANDSEPARATION OF THE LAYERS UPON HEATING THE METAL PRODUCT AT ELEVATEDTEMPERATURES COMPRISING A FIRST METAL FORMING A BASE, A THIN LAYER OF ASECOND METAL ADHERED TO SAID BASE BY EXPOSING THE BASE TO AN ATMOSPHEREOF GASEOUS CARBONYL FORMED FROM SAID SECOND METAL AND HAVING A THICKNESSOF BETWEEN ABOUT 0.00001 AND 0.00025 INCH, SAID THIN LAYER BEING OFGREATER POROSITY THAN SAID BASE METAL, AND HAVING THE GAS THEREINDESORBED THEREFROM, AND A FURTHER LAYER OF SAID SECOND METAL DISPOSEDOVER SAID THIN POROUS LAYER BY EXPOSING SAID THIN LAYER TO AN ATMOSPHEREOF GASEOUS CARBONYL FORMED FROM SAID SECOND METAL, SAID FURTHER LAYERBEING SUBSTANTIALLY GREATER IN THICKNESS AND HIGHER IN DENSITY THAN SAIDTHIN METAL LAYER, AND OF A THICKNESS OF AT LEAST 0.0004 INCH.